This invention relates to a magnetic head loading apparatus for loading and unloading magnetic heads on and from a magnetic recording medium, especially a magnetic disc.
The papers entitled "IBM Series/1 4964 Diskette Unit and Attachment Feature Theory Diagrams" published by IBM Corporation in 1977, discloses a conventional example of this kind of apparatus.
Among random access memory devices, there is a memory device called "Floppy Disc" using as a recording medium a flexible disc coated with magnetic material. The floppy disc memory apparatus using such a floppy disc has one or plural magnetic heads mounted in gimbal structure and data is recorded or reproduced by loading the magnetic heads on the floppy disc. When recording or reproduction is not executed, the magnetic heads are disposed at a distance from the surface of the recording medium, i.e. in the unload position, while they are shifted to the load position allowing them to be urged against the surface of the recording medium if the recording or reproducing operation is required.
Usually, the head load time (the time required for the head to move from unload to load position) must be as short as not more than 50 msec. One of the measures to reduce the head load time is to increase the speed at which the head is shifted from unload to load position. With that mechanism, however, since the speed of the head dashing against the recording medium is very high, there is caused a risk that the surface of the recording medium is damaged by the collision impact. For the recording medium there may be used a flexible material such as a Mylar sheet (polyethylene terephthalate film) coated with magnetic material. A solenoid is usually used to shift the magnetic head from unload to load position. It has a mechanical characteristic that the mechanical force it generates on a plunger member is minimum at the start of energization and maximum at the end of its movement. The magnetic head designed to be driven by a solenoid gains acceleration after the energization of the solenoid at the unload position and accelerates until it reaches the load position, colliding there at its maximum speed. This increases the chance of the magnetic recording medium being damaged and worn off.
Another method for shortening the head load time is to make the unload and load positions very close to each other. With this geometry, the head shift speed can be slowed down so that the collision impact can be moderated and damage to the medium surface can be prevented. However, this method also has a drawback. For the very close distance between the magnetic head and the magnetic recording medium may cause accidental collisions between them due to the vibrations caused by external disturbances and/or the vibrations of the motor for rotating the recording medium even if the head is stationary in the unload position. This adverse collision contact may also cause damage to the recording medium with considerably high probability.
The present trend is toward the adoption of the last method with an attempt to solve the inherent problem.